Devlog v0.15

Version 0.15 changes:

• SVG loading improvements to support creating stuff in Inkscape
• editing constraint names was broken
•  visually label the A/B verts of constraints
• further streamlined svg output
• composite statics would crash the sim builder. There's no reason to make composite statics, but that doesn't mean it should crash either!
• fixed crashes for tiny bezier lines
• recalculate the restLength of a damped spring by typing a negative number into the box (basically just type a - at the start of the line)
• added "save as level" which outputs a binary file. I'm still organizing all the workflow stuff for a future release, but if you want the loader code for this file format early, let me know!
• Many improvements to "save as code"